Known from German Pat. No. 2,731,001 is a round plug sleeve with an override spring, which has two contact-spring arms, against which two override-spring arms press from the outside. The contact-spring arms and the override-spring arms are not symmetrically spaced around the periphery, so that, effectively, only a one-sided contact can be established. This round plug sleeve is not amenable to miniaturization, since the asymmetrical spring action will not guarantee a secure contact. In the case of this known round plug sleeve, the override spring has locking-spring arms which snap behind a locking edge in a plug housing. These locking-spring tongues represent obstacles when used in a locking plug housing, since, at a minimum, they make it difficult to remove the round plug sleeve from the housing after unlocking and, in addition, would tend to destroy, during their withdrawal, a rubber seal placed, e.g., in the insertion aperture of a compartment of the plug housing. Furthermore, it is practically impossible to equip miniaturized round plug sleeves with catch-spring tongues.
Additionally, round plug prongs are known with longitudinally sequential sections consisting of a crimp section at the rear end, then a connection section followed by a support section, and a hollow, cylindrical section with a rounded point at the front end. For a miniaturized configuration and for use in a lockable plug housing, the known round plug prongs are not suitable, since the transition zones from the crimp section to the support section and from the support section to the round point section are not sufficiently stable to resist moments of flexion.
Also known is a lockable plug housing with two side walls, two end walls, and housing compartments separated by partitions. At least one compartment partition paralleling the side walls, which has matching holes in the longitudinal direction for the insertion of a locking slide, extends from one end wall to the other. The bar-like locking slide can be advanced into a matching hole in the end wall of the housing. It has laterally projecting cams, which, in the inserted state, protrude into the inner space of a compartment and snap behind an edge or the like of a plug sleeve or a plug prong, so that the plug contact is seated in the compartment of the housing and secured against withdrawal.
The installation and/or replacement of plug contacts already crimped to electric conductors requires careful attention and painstaking effort. The plug contacts are loose inside a compartment and have therein no restraints to prevent their removal or falling out; only the cams of the subsequently inserted locking slide provide such restraint. The known plug contacts insertable in the housing compartment have, for the most part, a sharp cornered cutting edge behind which a cam of the locking slide engages. When the plug contact is withdrawn, this sharp edge can destroy the rubber seal. In addition thereto, the known plug contacts have still other sharp projections, which can also damage the rubber seal even during the insertion of the plug element into the compartment of the housing.